(1). Field of the Invention
The present invention relates to a device to provide lateral and vertical displacement of a towed underwater cable and more particularly to a durable lightweight device for displacing an underwater cable which will not create excessive noise as the cable is towed through the water.
(2). Description of the Prior Art
The inventive device has characteristics in common with two other classes of devices, paravanes and depth control systems. Paravanes displace towed cables in a lateral direction away from the path of the towing craft. Depth control systems provide displacement in a vertical direction above or below the towing craft.
It is well known in the art that paravanes are used to provide displacement for towed cables lateral to the motion of the towing craft. Paravanes are towed bodies affixed at the end or along the length of a towed cable to position the cable away from the path of the towing craft. A fin or vane on the paravane causes a lateral displacement of the cable by producing lift in a lateral direction. Prior art paravane systems depend on components other than the vane itself to set and stabilize the direction of the hydrodynamic force. The stabilizing components used in prior art devices include attachment bridles, surface floats on tethers, net floats and trawl chains. These components increase size, weight, drag and noise thereby limiting use of these paravanes to low speeds in sonic operations.
Because many prior art paravanes are large or mechanically complicated devices, they must be removed from the water separately as the tow cable is retracted. Larger paravanes require the use of a hoist to remove them from the water. More complicated paravanes are less sturdy and must be treated with care to avoid damaging their inner workings.
Depth control devices are also well known in the art. Many mechanisms exist for controlling the depth of a towed underwater cable. These methods include diving planes, retractable vanes, air diaphragms, and movable horizontal plates. Adjustable diving planes are often used in the prior art to control the depth of the cable. Vertical displacement is achieved in some prior art devices by changing the buoyancy of the depth control device to maintain the desired depth.
Two prior art patents, Cole U.S. Pat. No. 3,375,800 and Cole U.S. Pat. No. 3,931,608, disclose depth control device that are rotatably mounted on towed acoustic cables. Cole '800 discloses a device mounted around the towed cable that utilizes ballast to maintain the depth control device in its preferred orientation and to prevent spinning. Cole '608 discloses a device mounted to the cable by rotatable brackets in such a way that the device hangs below the cable thus allowing the weight of the device to act as ballast. Both of these devices use pressure sensing means and adjustable diving planes to control depth. Neither of these devices provides for lateral displacement of a towed acoustic cable.
These prior art devices suffer the same durability problems as the more complicated paravanes. Furthermore, none of the known prior art devices are lightweight or simple enough to be wound onto a storage winch or reel with a towed acoustic cable.